According to the above-identified patent a construction machine is disclosed having a main frame supported by means of three or four vertically adjustable suspension points from a pair of walking beams located on opposite sides of the main frame. A vertical steering axis is provided at the ends of each walking beam connected to a bogey-mounted self-propelled ground engagement means in the form of a wheel or endless track.
One of the walking beams called the modified beam is connected to its side of the main frame by two spaced adjustable suspension means that are attached to the beam by pivotal bogey-mounts. One of the adjustable suspension means is attached to the frame rigidly in a vertical position while the other is pivotally mounted to the frame on a horizontal axis. The other walking beam is standard and is connected to the opposite side of the main frame on a single central vertically adjustable suspension means through a central pivot on a bogey-mount. The combination forms a three-point suspension for the frame on the walking beams. The four ground engagement means are attached to the ends of the walking beams in steerable pairs, in unison or individually so that it is possible to run the machine in any direction in relation to the plane of the main frame.
This basic construction also includes the use of two such modified walking beams having adjustable suspension means at each of their ends, both of which are horizontally pivoted to the frame on opposite or diagonal corners of the frame to form a four-point suspension. These embodiments whether three-point or four-point suspension, support the main frame well above the ground engagement means so both side-mounted and straddle-mounted tools can be used. The steering of each ground engagement means about its vertical steering axis at the end of its respective walking beam is accomplished by means of steering rams that connect from the saddle or bogey-mount to a spaced position along the walking beam. Extension or retraction of the ram rotates the bogey-mount and tractor on its vertical steering axis. Sequential attachment of one end of a ram to circumferentially spaced ears or lugs on the bogey-mount allows one ram to be used in turning a tractor 90.degree. or more. This result can be accomplished using motor-drive and a ring and pinion gear arrangement for full 360.degree. turning of a tractor. The actuation of the steering rams in pairs is coordinated by a servo-valve controlled hydraulic system or through a belt driven homing type sensor and feedback unit connecting two of the tractors and thereby sending a corresponding signal from one tractor for response by the opposite tractor through their respective steering rams or steering motors.